A 12 bit Non-Uniform Sampling SAR ADC Using Switchable Sampling Frequency

In this study, a frequency-division based successive approximation register analog-to-digital converter (SAR ADC) with two tone input signals and 12-bit resolution is developed in 0.18μm CMOS technology. The sampling frequency is 24 KHz. The base of this concept is non-uniform sampling achieved by phase/frequency detectors, frequency divider blocks, and up/down thermometer counter. In this design, the power consumption of the data converter is significantly lowered without sacrificing the linearity of the system by decreasing the sample frequency when the input signal will be slow down, such as biological signals that do not change frequently. At a 1.8 V supply, a factor of merit (FOM) of fJ/conversion 6.95 is attained.